Waterborne 2k coating composition having good pot life

ABSTRACT

A waterborne coating composition comprising at least one base neutralized active hydrogen containing film-forming resin and a water dispersible carbodiimide crosslinker capable of reacting with the film-forming resin to form a crosslinked film.

FIELD OF THE INVENTION

[0001] The present invention relates to waterborne coating compositions,especially base neutralized waterborne coating compositions havingcarbodiimide crosslinkers.

BACKGROUND OF THE INVENTION

[0002] Waterborne coating compositions are in demand in the automotiverefinish market due to increasingly strict environmental regulations. Asit relates to the present invention, waterborne coating compositions canbe utilized in two ways. The first utilization is as part of a two layercoating system comprising a basecoat layer and a clearcoat layer(“basecoat plus clearcoat system”). The second utilization is as asingle coating layer (“direct gloss system”).

[0003] A commercially acceptable waterborne coating composition for theautomotive refinish market must satisfy certain requirements. Theprimary requirements are as follows. The waterborne coating compositionmust cure at ambient temperatures or slightly higher and demonstrategood pot life, good water resistance, etc. To date, it has been verydifficult to formulate waterborne coating compositions that meet therequirements of the automotive refinish market.

[0004] In an attempt to improve certain performance properties ofwaterborne coating compositions, carbodiimide crosslinkers have beenincluded in the compositions. Although the inclusion of carbodiimidecrosslinkers improves water resistance and other coating properties, thepot life of such compositions is poor. The present invention provides abase neutralized waterborne coating composition having a carbodiimidecrosslinker which exhibits improved pot life.

SUMMARY OF THE INVENTION

[0005] In one embodiment, the present invention is a waterborne coatingcomposition comprising:

[0006] a. at least one base neutralized active hydrogen containingfilm-forming resin; and

[0007] b. a water dispersible carbodiimide capable of reacting with saidfilm-forming resin to form a crosslinked film.

[0008] In another embodiment, the present invention is a waterbornecoating system comprising a clearcoat composition applied over awaterborne basecoat composition, the waterborne basecoat compositioncomprising:

[0009] a. at least one base neutralized active hydrogen containingfilm-forming resin;

[0010] b. a water dispersible carbodiimide capable of reacting with thefilm-forming resin to form a crosslinked film.

[0011] In yet another embodiment, the present invention is a multi-layercomposite coating comprising a basecoat formed from a waterbornebasecoat film-forming composition and a clearcoat formed from aclearcoat film-forming composition applied over the basecoat, thewaterborne basecoat film-forming composition comprising:

[0012] a. at least one base neutralized active hydrogen containingfilm-forming resin; and

[0013] b. a water dispersible carbodiimide capable of reacting with thefilm-forming resin to form a crosslinked film.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is a waterborne coating composition. Thewaterborne coating composition of the present invention comprises atleast one base neutralized active hydrogen containing film-formingresin. The descriptive phrase “base neutralized” indicates a base isutilized to neutralize the active hydrogen containing film-formingresin. Suitable bases include amines and inorganic bases like lithiumhydroxide and potassium hydroxide. Suitable amines include ammonia andany primary, secondary, and tertiary amines. Tertiary amines arepreferred.

[0015] The base is usually present in the waterborne coating compositionin an amount necessary to neutralize the active hydrogen containingfilm-forming resin from between 100 to 200 percent. A 100 percentneutralization means that the mole ratio of base to acid is 1:1, and a70 percent neutralization means that the mole ratio of base to acid is7:10.

[0016] The descriptive phrase “active hydrogen containing” indicates thefilm-forming resin must have a group capable of reacting with acarbodiimide group such as a carboxyl group, an alcoholic hydroxylgroup, phenolic hydroxyl groups, and thiols. Suitable active hydrogencontaining film-forming resins include polyesters, polyurethanes,acrylic polymers, polyamides, and polyethers. The polymers used as thefilm-forming resin of the present invention are prepared with unreactedcarboxylic acid groups to impart the requisite acid functionality.

[0017] Suitable acrylic polymers include copolymers containingcarboxylic acid groups and acid groups of sulfur and phosphorus. Theseacrylic polymers and ways of preparing them are well known in the art.For example, these acrylic polymers can be synthesized from acidmonomers and one or more alkyl esters of (meth)acrylic acid. Suitableacid monomers include: (meth)acrylic acid, maleic acid, fumaric acid,crotonic acid, itaconic acid, 2-sulfo ethyl methacrylate,2-acrylamido-2-methyl-1-propane sulfonic acid, (meth)acrylamido methylphosphonic acid, and 2-phosphoethyl (meth)acrylate. Monoalkyl esters ofmaleic acid, fumaric acid, and itaconic acid can also be used tosynthesize the acrylic polymers.

[0018] Suitable alkyl esters of acrylic acid or methacrylic acid includealiphatic or cycloaliphatic alkyl esters containing from 1 to 30 carbonatoms in the alkyl group; preferably 4 to 18 carbon atoms in the alkylgroup. Methyl methacrylate, ethyl methacrylate, butyl methacrylate,ethyl acrylate, butyl acrylate, 2-ethyl hexyl acrylate, and hydroxyethyl(meth)acrylate are all examples of suitable alkyl esters of(meth)acrylic acid.

[0019] Suitable acrylic polymers further include copolymers synthesizedfrom one of the abovementioned monomers and one or more of the followingpolymerizable ethylenically unsaturated monomers: vinyl aromaticcompounds such as styrene and vinyl toluene; nitriles such asacrylonitrile and methacrylonitrile; amides such as acrylamide andmethacrylamide; vinyl and vinylidene halides such as vinyl chloride; andvinylidene chloride and vinyl esters such as vinyl acetate.

[0020] Polyesters and alkyd resins which can be utilized as thefilm-forming resin of the present invention and methods of preparingthem are well known in the art. For example, the polyester can beprepared via condensation of polyhydric alcohols and polycarboxylicacids. Suitable polyhydric alcohols include ethylene glycol, propyleneglycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol,diethylene glycol, glycerol, trimethylol propane and pentaerythritol.Suitable polycarboxylic acids include succinic acid, adipic acid,azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid,tetrahydrophthalic acid, hexahydrophthalic acid and trimellitic acid.

[0021] Similarly to the above, polyesters and alkyd resins can be formedfrom acids of sulfur and phosphorus as is well known in the art.Suitable acids of sulfur and phosphorus include2-phosphonobutane-1,2,4-tricarboxylic acid, and 5-sulfo isophthalicacid.

[0022] Polyurethanes which can be used as the film-forming resin of thepresent invention and methods of preparing them are well known in theart. For example, the polyurethane can be prepared by reacting polyesterpolyols or acrylic polyols with a polyisocyanate such that the OH/NCOequivalent ratio is greater than 1:1. Suitable polyisocyanates arealiphatic polyisocyanates, aromatic polyisocyanates, and mixturesthereof.

[0023] Optionally, the active hydrogen containing film-forming resin canhave hydroxyl functionality. The hydroxyl functionality can beassociated with the carboxylic acid functional polymer or it can bepresent as a separate hydroxyl functional polymer. Examples of suitablehydroxyl functional polymers include acrylic polyols, hydroxylfunctional polyesters, and polyurethanes. Typically, the hydroxyl valueof the polymers ranges from 10 to 100 mg KOH per gram of resin solidsand are present in amounts ranging from 45 to 95 weight percent based onthe resin solids weight of the active hydrogen containing film-formingresin.

[0024] The active hydrogen containing film-forming resin of the presentinvention typically has the following characteristics. The activehydrogen containing film-forming resin typically has a weight averagemolecular weight greater than 1,000 as determined by gel permeationchromatography using a polystyrene standard. The active hydrogencontaining film-forming resin typically has a number average molecularweight greater than 500 as determined by gel permeation chromatographyusing a polystyrene standard. The active hydrogen containingfilm-forming resin typically has an acid value ranging from about 5 mgKOH/g to about 738 mg KOH/g or about 10 mg KOH/g to about 200 mg KOH/gor about 10 mg KOH/g to about 45 mg KOH/g.

[0025] The active hydrogen containing film-forming resin is usuallypresent in the waterborne coating composition in an amount ranging fromabout 10 to about 100 weight percent or about 45 to about 85 weightpercent where the weight percent is determined from the ratio of resinsolids in the active hydrogen containing film-forming resin to the totalresin solids of the composition.

[0026] The waterborne coating composition of the present invention alsocomprises a water dispersible carbodiimide crosslinker. The phrase“water dispersible” encompasses carbodiimide dissolved or dispersed inaqueous phase. In order to utilize certain carbodiimides in the presentinvention, it may be necessary to modify the carbodiimides to make themwater dispersible. Techniques for modifying carbodiimides to make themwater dispersible are well known in the art.

[0027] Suitable water dispersible carbodiimide crosslinkers include analiphatic or aromatic dinitrogen analogue of carbonic acid of thegeneralized structure: RN═C═NR₁ where R and R₁ are hydrogen, aliphaticor aromatic groups. The aliphatic groups comprise alkyl chains and caninclude a carbodiimide such as dicyclohexyl carbodiimide. Oligomeric orpolymeric carbodiimide crosslinkers can also be used.

[0028] The preparation of water dispersible carbodiimide crosslinkers iswell known in the art. Suitable water dispersible carbodiimidecrosslinkers can be prepared by incorporating minor amounts of an aminesuch as dimethyl aminopropylamine and an alkyl sulfonate or sulfate intothe carbodiimide structure. Suitable water dispersible carbodiimides canalso be prepared by incorporating polyethylene oxide or polypropyleneoxide into the carbodiimide structure.

[0029] Suitable water dispersible carbodiimides are commerciallyavailable. For example, Ucarlink XL-29SE, XL-20 commercially availablefrom Union Carbide and Carbodilite VO2-L2 commercially available fromNisshinbo Industries, Inc. can be used in the present invention.

[0030] The concentration of the dispersed carbodiimide in the aqueousmedium is usually at least 1 percent by weight based on the weight ofthe aqueous dispersion and usually from about 2 to 60 percent by weightbased on the weight of the aqueous dispersion.

[0031] In the waterborne coating composition of the present invention,the water dispersible carbodiimide crosslinker is typically present inamounts ranging from about 5 to about 50 or about 10 to 35 or about 15to 25, weight percent resin solids based on total resin solids.

[0032] Optionally, the waterborne coating composition of the presentinvention comprises a water dispersible polyisocyanate. The phrase“water dispersible” encompasses polyisocyanate dissolved or dispersed inaqueous phase. In order to utilize certain polyisocyanates in thepresent invention, it may be necessary to modify the polyisocyanates tomake them water dispersible. Techniques for modifying polyisocyanates tomake them water dispersible are well known in the art.

[0033] The water dispersible polyisocyanates can be blocked ornonblocked. Suitable blocking agents are well known in the art.

[0034] Suitable water dispersible polyisocyanates includemultifunctional isocyanates and diisocyanates. Suitable multifunctionalisocyanates include a wide variety of monomeric and oligomericpolyfunctional isocyanates. Examples include the biuret adduct of 3molecules of a diisocyanate with 1 molecule of water, the adduct of anat least trifunctional polyol with 1 molecule of a diisocyanate perhydroxyl equivalent, isocyanurate group-containing compounds,1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatoluene, and uretdione.

[0035] Suitable multifunctional isocyanates are commercially available.Bayhydur VPLS 2319, Desmodur N, Desmodur L, and Desmodur N3390 arecommercially available from Bayer Corporation. Tolonate HDB and TolonateHDT-LV are commercially available from Rhone Poulenc. And, Cythane 3160is commercially available from BASF Group.

[0036] Examples of suitable diisocyanates include toluene diisocyanate,4,4′-methylene-bis(cyclohexyl isocyanate), isophorone diisocyanate, anisomeric mixture of 2,2,4- and 2,4,4-trimethyl hexamethylenediisocyanate, 1,6-hexamethylene diisocyanate, tetramethyl xylylenediisocyanate, 4,4′-diphenylmethylene diisocyanate.

[0037] The concentration of the dispersed polyisocyanate in the aqueousmedium is usually at least 1 and usually from about 2 to 60 percent byweight based on weight of the aqueous dispersion.

[0038] The amount of water dispersible polyisocyanate in the waterbornecoating composition typically ranges from about 5 to about 50 or about10 to 40 or about 15 to 35 weight percent resin solids based on totalresin solids.

[0039] In one embodiment of the present invention, the waterbornecoating composition is utilized as a single coating. A subsequentcoating layer is not applied over the single coat. In the industry, thisis referred to as a “direct gloss” system.

[0040] When the waterborne coating composition of the present inventionis used in a direct gloss system, the composition can include certainadditives to ensure the composition has sufficient durability and gloss.Conventional additives include pigments, UV absorbers, hindered aminelight stabilizers, flow additives, and solvents. All of theaforementioned additives are well known in the art.

[0041] In another embodiment of the present invention, the waterbornecoating composition is part of a basecoat plus clearcoat coating system.The waterborne coating composition of the present invention is thebasecoat, and a clearcoat composition is applied over the waterbornecoating composition.

[0042] The clearcoat composition can be waterborne or solventborne.Suitable waterborne clearcoat compositions are well known in the art.Suitable waterborne clearcoat compositions include a film-forming resinand a crosslinker system capable of reacting with the film-forming resinto form a crosslinked film. Examples of suitable waterborne clearcoatcompositions are disclosed in U.S. Pat. No. 5,633,307 and U.S. Pat. No.5,652,294 which are hereby incorporated by reference.

[0043] Suitable solventborne clearcoats are also well known in the art.Suitable solventborne clearcoats include one or more film-formingmaterials and one or more crosslinking materials capable of reactingwith the film-forming materials to form a crosslinked film. Examples ofsuitable solventborne clearcoats are disclosed in U.S. Pat. No 5,196,485and U.S. Pat. No. 5,814,410 which are hereby incorporated by reference.

[0044] The waterborne coating composition of the present invention canbe applied onto a substrate in the following manner. First, thewaterborne coating composition is applied to at least a portion of thesubstrate which is to be coated. The waterborne coating composition canbe applied by conventional means including brushing, dipping, flowcoating, spraying, etc. Depending on the type of coating system, thewaterborne coating composition may be cured via ambient or thermalmeans. Typically, the dry film thickness of the cured waterborne coatingcomposition ranges from about 0.1 mils to about 2.0 mils or 0.3 mils toabout 1.5 mils.

[0045] If the waterborne coating composition of the present invention isbeing used in a basecoat plus clearcoat system, after the waterbornecoating composition is applied to the substrate, the clearcoatcomposition is applied over the waterborne coating composition. Thecoating system is then cured via ambient or thermal means. Typically,the dry film thickness of the cured clearcoat composition ranges fromabout 1.0 mil to about 5.0 mils or 1.8 mils to about 3.0 mils.

[0046] The waterborne coating system of the present invention can beapplied to various substrates including wood, metal, glass, cloth,polymeric substrates and the like. The waterborne coating system of thepresent invention is particularly useful for coating metals andelastomeric substrates that are found on motor vehicles.

EXAMPLES

[0047] The present invention will be further illustrated by thenon-limiting examples below. Table 1 contains formulation data forwaterborne coating compositions according to the present invention.Table 2 describes the crosslinker system utilized in the exemplarycoating systems. Table 3 lists the pot lives of various crosslinkedwaterborne coating systems.

[0048] The exemplary coating compositions according to the presentinvention were prepared by taking 100 g of a commercially availablebasecoat composition and then adding a certain amount of base. Amine wasused as the base in the exemplary compositions. The basecoat and aminewere then mixed to form the coating composition of the presentinvention. Specific compositional information for the Examples is shownbelow in Table 1. TABLE 1 The Waterborne Coating Composition of thePresent Invention Dimethyl Ethanol % Approximate Example Amine²Neutralized⁵ pH⁶ T408 Black BC¹ 1 100 g None 77.1 7.24 2 100 g 0.10 g93.2 8.28 3 100 g 0.20 g 109.2 8.58 4 100 g 0.25 g 117.2 8.76 5 100 g0.30 g 125.2 8.92 6 100 g 0.35 g 133.3 9.04 7 100 g 0.40 g 141.3 9.10 8100 g 0.50 g 157.3 9.24 T413 Blue BC³ 9 100 g None 95.2 7.71 10 100 g0.20 g 122.0 8.70 11 100 g 0.50 g 162.0 9.17 T400 White BC⁴ 12 100 gNone 90.9 8.25 13 100 g 0.20 g 113.6 8.74 14 100 g 0.50 g 147.6 9.25

[0049] TABLE 2 Crosslinker Systems Utilized in the Exemplary CoatingSystems The following components were mixed together to form thecrosslinker systems used in the exemplary coating systems. CrosslinkerCrosslinker Component System #1 System #2 Bayhydur VPLS 2319¹/PMacetate² Blend 2.0 (3:1 by weight) UCARLNK XL-29SE³ 2.5 2.5 DeionizedWater 25.5 27.5

[0050] TABLE 3 Exemplary Waterborne Coating Systems Coating CompositionAmount of of Coating Crosslinker Amount of Example Composition System #Crosslinker Potlife¹ 1 70 g 1 30 g 10 minutes 2 70 g 1 30 g 45 minutes 370 g 1 30 g 75 minutes 4 70 g 1 30 g 75 minutes 5 70 g 1 30 g 120minutes 6 70 g 1 30 g 120 minutes 7 70 g 1 30 g 120 minutes 8 70 g 1 30g 120 minutes 1 70 g 2 30 g 3 minutes 2 70 g 2 30 g 30 minutes 3 70 g 230 g 60 minutes 4 70 g 2 30 g 100 minutes 5 70 g 2 30 g 120 minutes 6 70g 2 30 g 210 minutes 7 70 g 2 30 g 300 minutes 8 70 g 2 30 g >300minutes 9 70 g 1 30 g 30 minutes 10 70 g 1 30 g 150 minutes 11 70 g 1 30g >180 minutes 12 70 g 1 30 g 180 minutes 13 70 g 1 30 g >240 minutes 1470 g 1 30 g >240 minutes

[0051] Conclusions

[0052] The present invention provides a waterborne coating compositionhaving good pot life. As shown in Table 3 above, the pot-life ofcrosslinked waterborne coating compositions according to the presentinvention can be increased by increasing the % neutralization of thewaterborne coating composition.

What is claimed:
 1. A waterborne coating composition comprising: a. atleast one base neutralized active hydrogen containing film-formingresin; and b. a water dispersible carbodiimide crosslinker capable ofreacting with the film-forming resin to form a crosslinked film.
 2. Thecoating composition according to claim 1 whereby the totalneutralization of the base neutralized active hydrogen containingfilm-forming resin is between 100 to
 200. 3. The coating compositionaccording to claim 1 wherein the active hydrogen containing film-formingresin is selected from the group consisting of polyesters,polyurethanes, acrylic polymers, and mixtures thereof.
 4. The coatingcomposition according to claim 1 further comprising a water dispersiblepolyisocyanate.
 5. The coating composition according to claim 4 whereinthe amount of water dispersible polyisocyanate in the waterborne coatingcomposition ranges from about 5 to about 50 weight percent resin solidsbased on total resin solids.
 6. The coating composition according toclaim 1 wherein said active hydrogen containing film-forming has anumber average molecular weight greater than 500 as determined by gelpermeation chromatography using a polystyrene standard.
 7. The coatingcomposition according to claim 1 wherein said active hydrogen containingfilm-forming resin is present in the waterborne coating composition inan amount ranging from about 10 to about 100 weight percent determinedfrom the ratio of resin solids in the active hydrogen containingfilm-forming resin to the total resin solids of the composition.
 8. Thecoating composition according to claim 1 wherein said water dispersiblecarbodiimide crosslinker comprises an aliphatic dinitrogen analogue ofcarbonic acid of the generalized structure: RN═C═NR₁ where R and R₁ arehydrogen, aliphatic or aromatic groups.
 9. A waterborne coating systemcomprising a clearcoat composition applied over a waterborne coatingcomposition, the waterborne coating composition comprising: a. at leastone base neutralized active hydrogen containing film-forming resin; andb. a water dispersible carbodiimide crosslinker capable of reacting withthe film-forming resin to form a crosslinked film.
 10. The coatingsystem according to claim 9 whereby the total neutralization of the baseneutralized active hydrogen containing film-forming resin is between 100to
 200. 11. The coating system according to claim 9 further comprising awater dispersible polyisocyanate.
 12. The coating system according toclaim 9 wherein the active hydrogen containing film-forming resincomprises an acrylic polymer.
 13. The coating composition according toclaim 9 wherein said active hydrogen containing film-forming resin ispresent in the waterborne coating composition in an amount ranging fromabout 10 to about 100 weight percent determined from the ratio of resinsolids in the active hydrogen containing film-forming resin to the totalresin solids of the composition.
 14. The coating system according toclaim 9 wherein said water dispersible carbodiimide crosslinker ispresent in an amount ranging from 5 to 10 weight percent based on totalresin solids.
 15. A multi-layer composite coating comprising a basecoatformed from a waterborne coating film-forming composition and aclearcoat formed from a clearcoat film-forming composition depositedover the basecoat, the waterborne coating film-forming compositioncomprising: a. at least one base neutralized active hydrogen containingfilm-forming resin; and b. a water dispersible carbodiimide crosslinkercapable of reacting with the film-forming resin to form a crosslinkedfilm.
 16. At least a portion of a substrate coated with a multi-layercomposite coating comprising a basecoat formed from a waterborne coatingfilm-forming composition and a clearcoat formed from a clearcoatfilm-forming composition deposited over the basecoat, the waterbornecoating film-forming composition comprising: a. at least one baseneutralized active hydrogen containing film-forming resin; and b. awater dispersible carbodiimide crosslinker capable of reacting with thefilm-forming resin to form a crosslinked film.
 17. The coatingcomposition according to claim 16 wherein said active hydrogencontaining film-forming resin has a weight average molecular weightgreater than 1,000 as determined by gel permeation chromatography usinga polystyrene standard.
 18. The coating composition according to claim16 wherein said active hydrogen containing film-forming resin typicallyhas a number average molecular weight greater than 500 as determined bygel permeation chromatography using a polystyrene standard.
 19. Thecoating composition according to claim 16 wherein said water dispersiblecarbodiimide crosslinker comprises an aliphatic dinitrogen analogue ofcarbonic acid of the generalized structure: RN═C═NR₁ where R and R₁ arehydrogen, aliphatic or aromatic groups.